Oracle Team USA maneuvers in front of the Golden Gate Bridge before Sunday’s 14th race against Emirates Team New Zealand at the America’s Cup sailing eventin San Francisco.

SAN FRANCISCO — This has become the America’s Cup that just won’t end, thanks to fickle wind and Oracle Team USA’s remarkable resurgence.

Twice down by seven races, the defending champions from the United States no doubt have all of New Zealand on edge, including the thousands of Kiwis who pack the waterfront to cheer on the boys aboard Emirates Team New Zealand.

Skipper Jimmy Spithill and his mates with Oracle Team USA were masterful in tricky conditions Sunday on San Francisco Bay, winning Races 14 and 15 to cut the Kiwis’ lead to 8-5.

Spithill steered his 72-foot catamaran to huge leads in both races before the Kiwis cut the margin on the fourth leg. It was a day for back slaps and fist pumps aboard Oracle Team USA, which has won four straight since the Kiwis reached match point on Wednesday.

Backed by software tycoon Larry Ellison’s fortune, Oracle needs four more wins to keep the oldest trophy in international sports.

Oracle has won seven races. But it was docked two points as part of the harshest penalties in the 162-year history of the America’s Cup for illegally modifying boats in warmup regattas called the America’s Cup World Series.

Spithill hasn’t wavered since Oracle was penalized four days before the racing started, including having wing sail trimmer Dirk de Ridder tossed from the regatta.

“The boat is just so much quicker than when we started this competition,” said Spithill, 34, an Australian who lives in San Diego with his American wife and their two young boys. “We believe we can win this. We believe we’ve got the boat to do it, we’ve got the team, and we’ve got a wave of momentum that’s becoming bigger every day, behind us.”

The Kiwis, backed in part by their government and several corporate sponsors, still need just one win to spirit away the Auld Mug.

It’s gotten to the point that Barker was asked by a countryman if he can assure New Zealanders that they’re not watching Team New Zealand choke.

“Tough question,” said Barker, the hard-luck loser in the 2003 America’s Cup, who answered in his usual calm demeanor.

“We have absolute belief that we can win this and nothing’s changed,” the 41-year-old Barker said. “The numbers are still definitely in our favor, but that’s not what we’re going to rest on. We’re going to go out there tomorrow to perform as well as we possibly can. If we put everything together well, then we’ll win a race. If we don’t sail well, then that leaves an opportunity for the Oracle guys to win. We’re very, clear and very, very focused, and we’ll go out there tomorrow to do the best we can.”

Race 16 and Race 17, if necessary, are scheduled for Monday.

Oracle has won six of the last eight races and six of 10 since Spithill replaced American tactician John Kostecki with British Olympic star Ben Ainslie, who had been the helmsman of the backup boat. Ainslie, who won his fourth straight Olympic gold medal in 2012, and strategist Tom Slingsby, an Australian who won his first gold medal, are combining to make the right calls.

“There’s no question that was one of hardest days out there and clearly those guys nailed it,” Spithill said.

Oracle Team USA has made changes to its catamaran every night. Team CEO Russell Coutts — a New Zealander who has won the America’s Cup four times — said the crew has improved its technique sailing downwind.

“The changes to the boat are a big deal,” Spithill said. “They’re a big deal in terms of actual performance that you see physically, but also mentally for the crew because now the crew, they can see the boat is up to it. And they believe that they can do it and the boat can do it.”

Oracle Team USA looked like a rocket ship sailing downwind on its hydrofoils, its hulls completely out of the water.

The American boat even foiled sailing upwind on the third leg of Race 15 at about 35 mph.

Barker was slightly ahead at the start of Race 15 but had a little skid heading across the wind, which helped allow Spithill to reach the first mark first and round with a 3-second lead. Sailing downwind, Oracle opened a lead of some 765 yards.

There was a heart-stopping moment when Oracle sailed into a wind shadow and slowed dramatically as it passed Alcatraz Island and approached the top mark. The Kiwis closed to about 100 yards, but then they lost their wind and Spithill surged around the fourth mark and sped across the wind on its foils to the finish line just off America’s Cup Park on Pier 27-29.

There was a close call during the prestart when Oracle tacked quickly on favored starboard tack and the Kiwis crossed just ahead on port. Spithill protested but it was waved off.

The conditions on San Francisco Bay have already cost the Kiwis the chance to clinch the Cup. On Friday, Race 13 was abandoned because of the 40-minute time limit with the Kiwis well ahead on the fourth leg in light breeze. When the wind rose and the race was re-sailed, Oracle won to stay alive.

In Race 14, Spithill controlled the start and kept his black cat ahead the whole race, sometimes leading by well more than 300 yards.

The Kiwis closed to within about 30 yards when the boats crossed on the windward third leg as they zigzagged toward the Golden Gate Bridge.

Oracle made an extra tack at the top of the leg in order to make a left turn at the third gate mark and go farther offshore. Leading by 15 seconds at the mark, the American-backed boat — which has only one American on its 11-man crew — again opened a lead of more than 300 yards.

New Zealand closed again, but then sailed into a lighter breeze and Spithill raced ahead.

This America’s Cup is tied with the 2003 regatta in Auckland as the longest ever, at 16 days.

Spithill said Oracle is still the underdog and that his crew has performed better under extreme pressure.

“For the guys on board, they’re almost excited about the challenge. With this sort of wave of momentum, it’s truly swung over our way, we feel, and we’re going to keep riding it,” he said.

Said Barker: “You can easily get sort of caught up and frustrated and everything else, but it doesn’t help you sail any better. We have absolute belief that we can win and we’re looking forward to tomorrow now.”